Optical device including optically anisotropic molecules having intermediate pretilt angles

Abstract

An optical element is provided. The optical element includes an optical film including a birefringent material having a chirality. Optically anisotropic molecules of the birefringent material disposed adjacent a first surface of the optical film are configured with a first pretilt angle in a range of greater than 10° and less than 80°, or in a range of greater than −80° and less than −10°. Optically anisotropic molecules of the birefringent material disposed adjacent a second surface of the optical film opposing the first surface are configured with a second pretilt angle in the range of greater than 10° and less than 80°, or in the range of greater than −80° and less than −10°.

What is claimed is: 
     
       1. An optical element, comprising:
 an optical film including a first birefringent material layer and a second birefringent material layer, each birefringent material layer including a birefringent material having a chirality, 
 wherein:
 optically anisotropic molecules in the first birefringent material layer disposed adjacent a surface of the first birefringent material layer are configured with a first pretilt angle in a range of greater than 10° and less than 80°, or in a range of greater than −80° and less than −10°, 
 optically anisotropic molecules in the second birefringent material layer disposed adjacent a surface of the second birefringent material layer are configured with a second pretilt angle in the range of greater than 10° and less than 80°, or in the range of greater than −80° and less than −10°, 
 in each birefringent material layer, the optically anisotropic molecules disposed adjacent the surface, are configured with the same orientation, 
 each birefringent material layer includes a helix twist structure formed by tilted optically anisotropic molecules arranged in the thickness direction, the helix twist structure has a helical axis that is parallel with the thickness direction of the optical film, and 
 
 the first pretilt angle is different from the second pretilt angle. 
 
     
     
       2. The optical element of  claim 1 , wherein
 the first pretilt angle is in a range of greater than or equal to 30° and less than or equal to 40°, or in a range of greater than or equal to −40° and less than or equal to −30°, and 
 the second pretilt angle is in the range of greater than or equal to 30° and less than or equal to 40°, or in the range of greater than or equal to −40° and less than or equal to −30°. 
 
     
     
       3. The optical element of  claim 1 , wherein
 the first pretilt angle is in a range of greater than or equal to 25° and less than or equal to 50°, or in a range of greater than or equal to −50° and smaller than or equal to −25°, and 
 the second pretilt angle is in the range of greater than or equal to 25° and less than or equal to 50°, or in the range of greater than or equal to −50° and smaller than or equal to −25°. 
 
     
     
       4. The optical element of  claim 1 , wherein
 the surface of the first birefringent material layer is a first surface of the first birefringent material layer, the first birefringent material layer has a second surface opposing to the first surface, optically anisotropic molecules disposed adjacent the second surface are configured with a third pretilt angle in the range of greater than 10° and less than 80°, or in the range of greater than −80° and less than −10°, 
 the surface of the second birefringent material layer is a first surface of the second birefringent material layer, the second birefringent material layer has a second surface opposing to the first surface, optically anisotropic molecules disposed adjacent the second surface are configured with a fourth pretilt angle in the range of greater than 10° and less than 80°, or in the range of greater than −80° and less than −10°, and 
 the first pretilt angle and the third pretilt angle in the first birefringent material layer have different absolute values, and the second pretilt angle and the fourth pretilt angle in the second birefringent material layer have different absolute values. 
 
     
     
       5. The optical element of  claim 4 , wherein each of the first pretilt angle, the second pretilt angle, the third pretilt angle, and the fourth pretilt angle is in a range of greater than 30° and less than or equal to 40°, or in a range of greater than or equal to −40° and less than −30°. 
     
     
       6. The optical element of  claim 1 , further comprising an alignment structure coupled to the surface of the first birefringent material layer and configured to align the optically anisotropic molecules disposed adjacent the surface of the first birefringent material layer in the first pretilt angle. 
     
     
       7. The optical element of  claim 6 , wherein the alignment structure includes at least one of a nanostructure alignment layer including a random distribution of planar and vertical alignment polyimide domains, a photoalignment layer that includes nanostructured domains of planar and vertical alignment polyimides, a photoalignment layer, an alignment layer including a polyimide mixed with a liquid crystalline prepolymer, or a hybrid alignment polymer network. 
     
     
       8. The optical element of  claim 1 , wherein:
 the optically anisotropic molecules of the first birefringent material layer disposed adjacent the surface of the first birefringent material layer are exposed to air, and 
 the first birefringent material layer further includes surfactants or small weight molecules configured to align the optically anisotropic molecules exposed to the air in the first pretilt angle. 
 
     
     
       9. The optical element of  claim 1 , wherein in each birefringent material layer, the helix twist structure is a heliconical structure. 
     
     
       10. The optical element of  claim 9 , wherein the helix twist structure has a constant helix pitch. 
     
     
       11. The optical element of  claim 9 , wherein the helix twist structure has a gradient helix pitch. 
     
     
       12. The optical element of  claim 1 , wherein at least one of the first birefringent material layer or the second birefringent material layer is a liquid crystal polymer film. 
     
     
       13. The optical element of  claim 12 , wherein the birefringent material in the liquid crystal polymer film is polymerized. 
     
     
       14. The optical element of  claim 12 , wherein the birefringent material in the liquid crystal polymer film is polymer stabilized. 
     
     
       15. The optical element of  claim 1 , wherein the birefringent material includes active liquid crystals that are switchable by an external field. 
     
     
       16. The optical element of  claim 1 , wherein each birefringent material layer is a polarizing film configured to substantially reflect a polarized light having a handedness that is the same as a handedness of the helix twist structure, and substantially transmit a polarized light having a handedness that is opposite to the handedness of the helix twist structure. 
     
     
       17. The optical element of  claim 1 , wherein the optical film is configured to function as an optical diffuser for providing a directional scattering. 
     
     
       18. The optical element of  claim 1 , wherein:
 the surface of the first birefringent material layer is a first surface of the first birefringent material layer, the first birefringent material layer has a second surface opposing to the first surface, optically anisotropic molecules disposed adjacent the second surface are configured with a third pretilt angle in the range of greater than 10° and less than 80°, or in a range of greater than −80° and less than −10°, 
 the optical element further comprises a first alignment structure coupled to the first surface of the first birefringent material layer and configured to align the optically anisotropic molecules adjacent the first surface of the first birefringent material layer in the first pretilt angle; and 
 a second alignment structure coupled to the second surface of the first birefringent material layer and configured to align the optically anisotropic molecules adjacent the second surface of the first birefringent material layer in the third pretilt angle.